Author: Robert Hyatt
Date: 08:00:30 07/29/02
Go up one level in this thread
On July 29, 2002 at 00:28:05, J. Wesley Cleveland wrote: >On July 28, 2002 at 13:02:01, Robert Hyatt wrote: > >>On July 27, 2002 at 15:06:23, J. Wesley Cleveland wrote: >> >>>On July 25, 2002 at 20:13:45, Robert Hyatt wrote: >>> >>>>On July 25, 2002 at 19:24:06, J. Wesley Cleveland wrote: >>>> >>>>>I see that crafty does not store lower bounds of MATE-n in the hash table, >>>>>rather changes them to MATE-300. Bob wrote that he had search instabilities >>>>>before he did this. Normally, this does not matter, but I think it makes crafty >>>>>considerably slower in finding mates, as it only gets cutoffs on exact scores. >>>>>Do other people have experience in this ? >>>> >>>> >>>>Note that all this does is slightly decrease search efficiency. I do store >>>>_exact_ mate scores as they should be stored. I store "bounds" that are based >>>>on MATE as MATE-300. The penalty is _very_ small unless you have a position >>>>where almost everything leads to a forced mate of some sort... >>> >>>The place where I notice it is in engame analysis with EGTBs, where after a long >>>time the PV is scored as Mate in 38 or so, and then it takes a *very* long time >>>to prove the other root moves are worse. >>> >>>A related question: >>>If the score in the hash table is MATE-300 and this would cause a cutoff, >>>shouldn't you cut off even if the draft is not deep enough ? >> >> >>I could but I don't. That would prevent finding a _shorter_ mate the next >>iteration. > >But wouldn't you only care about a shorter mate if the _value_ would not cause a >cutoff ? There are two issues here: 1. absolute mate scores. I store those correctly, as is, corrected for the distance from the current position to the actual mate. 2. mate bounds. I found problems with those, and simply changed any mate bound to mate-300. It is still large enough to cause cutoffs against any possible material gain or loss. But not large enough to confuse a real mate search where the scores are absolute but the bounds are not...
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